A specific proteinase, called proteinase, I, has recently been isolated from the celluar slime mold, Dictyostellium discoideum. Evidence has been obtained which indicates that this enzyme contributes to the selective regulation of UDP glucose pyrophosphorylase turnover during differentiation of this organism. Studies outlined in this proposal are directed towards characterizations of (1) the mechanism of regulation of cellular proteinase I levels during differentiation, (2) a detailed analysis of the mechanism of degradation of UDPglucose pyrophosphorylase catalyzed by proteinase I, and (3) an analysis of the specificity of proteinase I for degrading other cellular enzyme of D. discoideum.